DESCRIPTION: In adults, the visual field extends to approximately 110 deg temporally, 60 deg nasally, 60 deg superiorly, and 75 deg inferiorly. Young human infants, however, show limited responsiveness to peripheral stimuli, yielding measured visual fields that extend temporally to only about 30 deg at birth and 45 deg at age three months. Among the few studies that have examined visual field extent after early infancy, there is disagreement as to the rate at which visual field development occurs. Studies that have used low temporal frequency targets suggest that visual field extent approaches adult values by age one year, whereas studies that have used high temporal frequency targets show more restricted visual fields at the end of the first postnatal year. The purpose of Part I of this proposal is to test the hypothesis that differences among studies in the measured rate of infants' visual field development are related to differences in the rate of development of the magnocellular (M) and parvocellular (P) pathways. Children 4, 7, 9, 17, and 30 months of age will be tested with low spatial frequency (3 deg and 0.7 deg diameter) stimuli that are either (a) low in temporal frequency (0,1, or 3 Hz), to stimulate the P pathway preferentially, or (b) high in temporal frequency (10 or 20 Hz), to stimulate the M pathway preferentially, to determine whether development of measured visual field size depends on stimulus parameters, as predicted from animal research on M and P pathways. Clinically, quantitative assessment of either central or peripheral visual fields is rarely undertaken in infants and toddlers. This is due to (1) a lack of knowledge about the development of peripheral vision, and (2) a lack of methodology for assessment of central and peripheral visual fields in individual infants and children. The purpose of Part II of this proposal is to use data from Part I to develop a quantitative procedure for screening of central and peripheral visual fields in infants and young children. Normative data and data on intra- and inter-observer test-retest reliability will be collected from 4-, 7-, 9-, 17-, and 30-month-olds. In summary, the proposed research will (1) further our understanding of the mechanisms underlying the expansion of measured visual field size in human infants, and (2) develop and begin to validate a procedure for assessment of central and peripheral visual fields in infants and toddlers.